1. Field of the Invention
The present invention relates to a process for removing silicon compounds from hydrocarbon solvents. More particularly, the invention relates to a process for removing residual silicon species from polymerization solvents.
2. Background of the Related Art
Solvents containing silicon compounds are by-products of polymerization processes for making telechelic polymers and also by-products of other manufacturing processes. Telechelic polymers include diols, triols and star polyols, which have found wide utility in many applications. Telechelic polymers have been employed as rocket fuel binders, in coatings and sealants and in adhesives, and can be co-polymerized with appropriate materials to form polyesters, polycarbonates, and polyamides.
In a typical polymerization process of telechelic polymers, a silicon compound is added to a diene monomer in a hydrocarbon solvent to initiate polymerization of the diene compound. A structure modifier may also be present. After polymerization is complete, a capping agent such as ethylene oxide may be added to introduce a terminal functional group. The polymer is optionally hydrogenated to reduce unsaturation. The resulting silicon compound such as a silyl ether is then hydrolyzed in the presence of an acid, and optionally an alcohol, to produce the desired telechelic polymer. During hydrolysis, residual silicon species are formed as by-products at lower concentrations either as impurities in the initiator, die-out products of the initiator, or side products of the hydrolysis. These residual silicon species can interfere with polymerization and, therefore, should be removed from the solvent before recycling the solvent for polymerization.
There remains a need to efficiently separate residual silicon species from hydrocarbon solvents. Using distillation to separate organic solvents from residual silicon species is difficult since the boiling points of the residual silicon species and solvents are only a few degrees apart. Direct distillation also incurs the risk of entraining other contaminants, like nitrogen compounds or sulfurous compounds, into the distillate.
The present invention generally provides a process for removing residual silicon species from hydrocarbon solvents by adsorbing the silicon species on a selective adsorbent. The process is useful for recovering solvent after producing telechelic polymers by polymerizing a monomer in a hydrocarbon solvent with a silicon compound. After the hydrocarbon solvent is separated from the polymer cement, the hydrocarbon solvent is purified in an adsorption bed containing the selective adsorbent. The hydrocarbon solvent is recovered and recycled to the polymerization process.